I did a full install of Home Premium
then "Anytime Upgrade" to Ultimate
WMP 11 plays DVDs just fine.
I'm guessing Mr. Urban, that you either bought a new PC with vista already
on it or upgraded from an XP install. In both cases teh computer would have
come with DVD decoders already installed (assuming dvds ran under XP). From
my own experience and that of everyone i've talked to, Vista does not come
with the necessary codecs to play DVDs.
To play a standard format DVD in the United States it is encoded as a
MPEG-2 file as preliminary step in order to conform to the NTSC
(National Television System Committee) standard of 29.97 interlaced
frames of video per second. See below link.
http://en.wikipedia.org/wiki/NTSC
Most of the rest of the world uses PAL another encoding scheme.
All MPEG-2 encoders/decoders are licensed by the MPEG Group who's full
name is the Moving Picture Experts Group.
http://www.chiariglione.org/mpeg/
If or not a DVD plays on your computer depends on if or not you have a
application installed that paid the licensing fee to the MPEG group
for the right to distribute a decoder/encoder based on the various
patents they hold. Bottom line, Microsoft is TOO CHEAP to include this
in the versions that don't support Media Center. I'm not even sure it
comes with versions that do have Media Center. So the business version
won't by itself play DVD's unless you have something ELSE in the way
of a third party application on your system that has paid the
licensing fee and has installed the necessary MPEG-2 CODEC.
http://en.wikipedia.org/wiki/Codec